Effects Of Rest Grazing In Different Stages Of Spring On Reproduction And Root Of Kobresia Capillifolia And Elymus Nutans In Alpine Meadow

Alpine meadow is an important grazing ecosystem in China,which plays critical roles in the development of pastoral productivity,the protection of biodiversity and the maintenance of ecological balance.However,due to global warming and anthropogenic disturbance,the alpine meadow of the Qinghai Tibet Plateau was seriously degraded,thus the degraded grassland is in urgent need of restoration.Rest grazing is the most economical and effective vegetation restoration way for degraded alpine meadow.Rest grazing often conducted in the returning green stage,while it is not clear whether rest grazing in the stage of soil thawing orbefore retuning green stage is more beneficial for grassland than in the returning green stage?In order to solve this problem,considering the factors of"soil"and"grass",a controlled grazing trial,with five rest grazing stage:critical stage of soil thawing,later stage of soil thawing,early stage of returning green,later stage of returning green,and local traditional rest grazing?as control?,was conducted on the eastern edge of the Qinghai Tibet Plateau for two years.In this study,the effects of different stages of spring rest grazing on the reproduction?sexual and vegetative?and root characteristics?quantitative characteristics,contents of nutrients,cellulose,proline and antioxidant system activity in storage?of Kobresia capillifolia and Elymus nutans were studied,we figured out the best rest grazing stage of alpine meadow in Qinghai Tibet Plateau,provided basis for sustainable utilization and scientific management of alpine meadow.The main results were as follows:1.The rest grazing in the thawing soil stage was beneficial to the sexual reproduction of the two plants,which is not conducive to their vegetative reproduction,however,the rest grazing in the later returning green stage and local traditional rest grazing were not conducive to the sexual reproduction of the two plants,while it was conducive to their vegetative reproduction.With the advance of rest grazing,the sexual reproduction ability of the two plants increased,the vegetative reproduction ability decreased,the reproductive strategy was changed from vegetative reproductive to sexual reproductive.Under the traditional rest grazing,the resource allocationof K.capillifolia mainly allocated for vegetative reproductive rather than root growth to,while under other stages rest grazing,the resource was mainly used for root growth.With the rest grazing in the critical stage of soil thawing,later stage of returning green and local traditional rest grazing,the resource allocation of E.nutans was mainly used for sexual reproduction instead of underground growth;with the rest grazing in the later stage of soil thawing,the resource allocation used for vegetative reproduction was transferred to sexual reproduction;with the rest grazing in the early stage of returning green,the resources was mainly allocated for underground growth.2.With the advance of rest grazing,the root biomass of K.capillifolia increased,while the root length and volume decreased;the root biomass,root length and root volume of E.nutans increased;the root storage substance content of both K.capillifolia and E.nutans decreased.The storage substance of the two plants was negative correlated with the root biomass of the respective roots.The content of PRO,MDA and the production rate of O₂^-in the roots of K.capillifolia and E.nutans were analyzed synthetically.It was found that the damage degree both of two plants was greatest with the rest grazing in the later stage of returning green and local traditional rest grazing,the damage degree was least with the rest grazing in the early stage of returning green.The activities of SOD,CST and ASA-POD in the roots of K.capillifolia decreased with the advance of rest grazing.3.According to the principal component analysis,the main evaluation indices of K.capillifolia were:ear length,1000-grain weight,root length,root volume,soluble protein,NDF,hemicellulose,MDA,ASA-POD;the main evaluation indices of E.nutans were:seed number per ear,1000-grain weight,tiller number,root volume,root diameter,soluble protein,hemicellulose,MDA,ASA-POD.The effect of membership function on the comprehensive evaluation of the rest grazing stage was as follows:the critical stage of soil thawing>the later stage of soil thawing>the early stage of returning green>the later stage of returning green>local traditional rest grazing.Therefore,we suggest it's better to start the rest grazing of spring in the critical stage of soil thawing of alpine meadow.